You cannot simply define a maximum bouncing time unless you know, how the contacts behave with the actual switched load! The same switch can behave totally different in terms of bouncing, when switching a resistive load or an inductive one! Also, if a switch contact is overrated, it can behave very strange after some switchings, resulting in an extreme increase of bounce time. Yes, even the refuse of further successful switchings can occur then!

So again: What loads do the relays switch? And what is the rating of these relays? Tell us the brand of relay, better though a link to datasheet.

Switch contacts can have problems with too light and with too heavy loads. So, take care, that you choose the proper relays for your application.

Kai